Myocardial injury during the anoxia associated with cardio-pulmonary by-pass is a cause of serious intra- and post-operative complications. Although methods to alleviate this problem are multiple, none are entirely satisfactory. The use of a biological agent to lower myocardial metabolism in a non-toxic reversible manner will be investigated as a protective agent against the myocardial injury of hypoxia. If it is successful, the effect will be compared with that obtained by the use of cardioplegic solutions alone. The assay system will consist of an isolated rat heart being perfused with oxygenated physiologic Salt Solution at 37 degrees C. Myocardial Contractility and oxygen comsumption parameters will be followed through periods of anoxia and re-oxygenation recovery. Increased tolerance to and enhanced recovery from hypoxia will be the indicators. If anti-metabolic brain extracts show a favorable influence as contrasted to control injections of other brain extracts, attempts to purify and isolate the active component of the extract will be made using standard biochemical techniques.